1. Field
The disclosed embodiments concern an improvement in superplastic press forming systems, particularly an advanced feed device for such a press forming system.
2. Brief Description of Related Developments
Superplastic press forming SPF is a method of forming strip or sheet-metal-based pieces to make complex, resistant light-weight pieces with very large extensions.
It is based on heating metal strips or sheets placed in a forming tool with a cavity and applying pressure with gas injected into the cavity of the tool to push the piece against the wall of the cavity of the forming tool.
For aluminum-based alloys, the temperature of the cavity must reach a value of 450° C. to 500° C. and for titanium-based alloys, the temperature must commonly reach 890° C. to 920° C.
An example of pressing and hot pressing by superplastic deformation is known from document US 2006/0260373 A1 and an example of a complex piece made by such a process is known from FR 2 739 832 A1.
A conventional press for forming simple sheet metal is sketched in FIG. 1 of the prior art.
The press includes a hot press slide 1, a cover 2, forming the top part of the cavity that holds and forms the piece 3, a forming tool 4 that fits into a bottom die 5 and a heating support forming the base 6 of the press.
The bottom part of the cover 2 and the top part of the forming tool form two hot-forming die halves between which the sheet metal 3 being formed is inserted.
A pressurized gas G is inserted into the cavity through one or more conduits 6 to apply pressure PG to the sheet metal 3 and push it against the forming tool 4.
When the piece is being formed, mechanical pressure PM is applied to the slide of the press to clamp the edge of the piece and seal the cavity.
One of the problems with the process is that the time for heating the various parts of the tool is very long, commonly two days to reach a high uniform temperature for the tool components, so the process can be used.
This is not really a problem when parts are made in large series with the same shape, since this heating time similar to the start-up time for the process is negligible compared to the time the tool is used.
Moreover, to increase the pace of the press, it is known how to preheat the pieces outside the press to prevent them from spending too long in transit to the press.
In this context, document US 2006/0237420 A1 describes a device for heating and transferring parts that makes it possible to feed the press with preheated parts.
This device has a transport shuttle for the metal strips or sheets intended to make the piece and means of heating the metal strips.
On the other hand, in the case of small series of pieces with different shapes, preheating the metal strips or sheets is not enough to optimize the yield of the process and, notably, the time necessary for preheating the die half of the forming tool becomes a disadvantage compared to the time for forming the pieces.
In addition, in such case, there is a need to let the forming tools cool to replace them, which adds to the time that the press is not available.
The heating and cooling phases in particular can represent up to 30% of the load on the press for small and medium-sized series.